SHIFT SOLENOID I THINK 3RD GEAR

2000 Ford Focus • 80,000 miles

While driving goes into 3rd gear but then when my to.S go up or I go over idk 30mph it disengaged then when let off gas or let rev down it engages again. Sounds like a solenoid but no codes? I need help nobody knows what it is here sounds like solenoid to me but why no codes any help would be very helpful.

Sometimes codes do not show because the solenoids are working correctly electrically but the mechnical side is leaking causing pressure drop. I would suggest checking the fluid condition and filter. If filter is partially clogged or level is low, insufficient fluid movement would cause symptoms as well.
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Ok fluid level is ok idk about filter yet don't want to drain fluid an take pan off to switch filter out then just to have to replace solenoid after an waste fluid when drain again an waste it. Isn't it a special type of fluid also. So other then fluid low or filter being clogge is there anyway way a solenoid could be malfunctioning without a code. Fluid looks clean so guessing filter is good also